Method: In a pot large enough to hold everything, saute vegetables in butter until tender, add thyme. Add flour all at once, stirring well to mix. Don't worry if the vegetables are broken in the process. Cook until raw smell is gone, 5 to 8 minutes. Whisk-in stock, tomato puree and bay leaf and simmer for at least 2 1/2 hours, skimming as necessary. Strain out solids as above and cool.
Espagnole sauce is usually made with beef, but this one is equally full-bodied and satisfying.
